The invention relates to a gear drive unit, particularly for a seat adjuster or a power-assisted steering system in a motor vehicle.
A device for adjusting a seat in a motor vehicle in known from EP 0 759 374 or DE 43 31 822, which is fastened on a base part, and is comprised of a spindle on which a drive gear that drives the spindle is provided, a drive assembly, which drives the drive gear by means of a driven element and at least one device on which the drive assembly is at least flanged-mounted and which operationally couples at least the driven element and the drive gear.
In the case of a seat adjuster motor with a spindle drive, a spindle is inserted into a gear housing, which is generally already connected to a motor. The inserted spindle is often executed as a composite part and is comprised in the simplest case of the spindle, a sprayed-on worm wheel and an axial point abutment, which is executed, e.g., as a ball. Additional add-on parts to the spindle, like a spindle nut, limit stop sleeve are conceivable. The spindle should be mounted as free of play as possible in the gear housing so that the operating forces on the spindle ideally do not cause any axial lift of the spindle in the gear housing. The lack of play is achieved as a rule by measuring the gear housing and inserting a matching thrust washer. The lack of play can be supported, e.g., by the additional insertion of a spring element. In order to optimize the friction conditions on the worm wheel, an axial bearing disc can also be mounted on the side opposite from the point abutment.
In addition to the operating forces that arise, spindle motors must also support crash forces (tensile and compressive forces), and depending upon the application case, the gear housing is therefore executed in plastic or metal. Future requirements are tending to lean towards higher crash requirements. In general, the metal housing required for this necessitates more expensive rework steps in order to comply with tolerances. In this case, a lateral opening that is designed to be vertical to the spindle axis for inserting the spindle has a fundamentally negative effect on the strength of the gear housing, i.e., the gear housing tends to bend open under tensile loads, After the spindle is mounted in the gear housing, the housing is closed by means of a gear cap, e.g., via screw down. The position of a customer-side connection borehole can be placed in different positions around the spindle axis. As a result, this often requires a new gear housing for each application.